1. Field of the Invention
The invention relates to a metering device for dry bulk material comprising at least one metering element driven by a rotary drive for feeding the bulk material from a storage container to at least one outlet.
2. Description of the Related Art
Metering devices in the form of metering screws, metering transfer canals, or metering disks for dry bulk material are known. They have the disadvantage that they do not have absolutely linear metering properties. The metering transfer canal exhibits always pulsation as a result of the individual metering chambers. A metering disk also has a pulsing action because of its metering holes. The metering screw pulses according to a sine curve because of the drop of the dry bulk material at the exit of the screw. When positioning the metering screw at a slant, the sine-shaped pulsation during removal of the metered dry bulk material can be reduced but not prevented.
In particular in discontinuously operating mixing devices, the irregular metering quantities have the disadvantage that, depending on the type of metering device, the concentration (proportion in percentage) of the individual components can exhibit short-term deviations as a result of pulsation. In connection with so-called batch mixing systems, the irregular metering action has the also the disadvantage that a defined weight or volume of dry bulk material cannot be metered with high precision. The imprecision of such systems results from the fact that, upon stopping the metering device, a chamber or a screw winding will not empty at all or will empty too much. The irregular metering quantities are particularly disadvantageous when small or even smallest quantities must be metered.
It is an object of the present invention to configure the metering device of the aforementioned kind such that a uniform and precise metered flow is ensured.
In accordance with the present invention, this is achieved in that the metering element transports the dry bulk material in a direction deviating from the horizontal direction and comprises at least one helical stay which during transport of the dry bulk material interacts with a pipe projecting into the lower area of the storage container.
In the metering device according to the invention, the material to be metered is engaged by the helical stay and is uniformly fed to the outlet. Advantageously, the metering element extends vertically. The material is then transported by the helical stay in the upward direction. By means of the metering device according to the invention, even smallest amounts of material can be metered with high precision. Fluctuations in the metering action do not occur as a result of the embodiment according to the invention.